This story was written by David Kaplan. WPP Group's 24/7 Real Media has formed a B2B online ad network with four media companies: Nielsen Business Media, Reed Business, McGraw-Hill (NYSE: MHP) and Cygnus Business Media. Although focused on B2B, the BBN, as the ad net is called, is comprised of a number of titles with very different audiences, such as Construction Equipment, Adweek, Aviation Week & Defense Technology and CPA Technology Advisor. 24/7 claims the network has a reach of nearly 10 million monthly uniques across roughly 200 websites. BBN plans to invite other B2B publishers to participate later this year. Derek Reisfield, former *CBS* exec and MarketWatch co-founder, is chairman of the new venture. Release